1. Field of the Invention
The present invention relates to a vibration damping device to be used, for example, for an engine mount, a body mount, a member mount and so forth of an automobile, especially to a fluid-filled vibration damping device using the vibration effect based on the flow action of a fluid sealed therein.
2. Description of the Related Art
Conventionally, as a type of vibration damping connector or vibration damping support interposed between the members constituting a vibration transmission system, there has been known a vibration damping device. The vibration damping device has a structure where a first mounting member and a second mounting member to be mounted to each of the members constituting the vibration transmission system are elastically connected to each other by a main rubber elastic body. A fluid-filled vibration damping device using the fluid flow action is also known as a vibration damping device. This fluid-filled vibration damping device has a structure where a pressure-receiving chamber and an equilibrium chamber are formed facing each other across a partition member supported by the second mounting member, and a non-compressible fluid is sealed in these pressure-receiving chamber and equilibrium chamber that are communicated with each other via an orifice passage. For example, the one disclosed in Japanese Unexamined Patent Publication No. JP-A-2009-243510 is such a device.
Meanwhile, in the fluid-filled vibration damping device, the vibration damping effect based on the fluid flow action is effectively exerted corresponding to a frequency vibration to which the orifice passage is tuned, whereas a valid vibration damping effect corresponding to a vibration frequency beyond the tuning frequency is hard to obtain. Especially because the orifice passage is substantially shut off due to antiresonance at an input of vibration at a higher frequency than the tuning frequency, there is a problem of degraded vibration damping performance due to a higher dynamic spring constant.
Such being the case, a liquid pressure transmission mechanism is built in the structure described in JP-A-2009-243510 provided with a fluid flow channel that allows transmission of liquid pressure between the pressure-receiving chamber and the equilibrium chamber. More specifically, this liquid pressure transmission mechanism with a movable member (movable plate) stored in a housing space formed in the partition member has a structure where liquid pressures of the pressure-receiving chamber and the equilibrium chamber are each applied to either side of the movable member via a communication hole (fluid flow channel) formed through the wall of the housing space. Then, the movable member undergoes a slight displacement or deformation at an input of high-frequency small-amplitude vibration to allow transmission of liquid pressure between the pressure-receiving chamber and the equilibrium chamber, while the movable member blocks the communication hole to prevent transmission of liquid pressure between the two chambers when vibration is inputted at a frequency in the range of tuning frequency of the orifice passage. This makes it possible to obtain the vibration damping effect exerted by the fluid flow through the orifice passage and the vibration damping effect exerted by the liquid pressure absorption effect of the liquid pressure transmission mechanism selectively and in an effective way.
However, the fluid-filled vibration damping device equipped with such a liquid pressure transmission mechanism tends to have a problem of striking noise generated by the impact force when the movable member comes into contact with the inner surface of the housing space. In other words, by causing the impact energy to be exerted on the vehicle body via the partition member and the second mounting member that supports it, there was a risk of abnormal noise generated in the vehicular cabin.